Continuously variable transmissions and differential combinations for vehicles have been under development for several years. These units have a driven input shaft with a first variable drive pulley, a driven shaft with a second variable drive pulley and a v-belt trained around the two pulleys. The first variable drive pulley on the input shaft has a fixed sheave and an adjustable sheave. The adjustable sheave is moved axially along the input shaft toward or away from the fixed sheave to change the effective diameter of the first variable drive pulley. The second variable drive pulley on the driven shaft includes a fixed sheave and an adjustable sheave that is moved axially along the driven shaft to change the effective diameter of the second variable drive pulley. The adjustable sheave of the second variable drive pulley is spring biased and hydraulically biased toward the fixed sheave so that the second variable drive pulley changes its effective diameter in response to changes in the effective diameter of first variable drive pulley and so that tension on the v-belt is maintained.
The driven shaft drives a reversible gear train. The reversible gear train drives a differential through a speed reduction system. The speed reduction system can be reduction gears or a chain trained around a drive sprocket and a driven sprocket. The differential drives the axle shafts that the wheels are mounted on.
The transmission input shaft is driven by a power source at substantially higher speed than the speed at which the axle shafts turn. The v-belt and the first and second variable drive pulleys drive the output shaft at speeds that are slower than, equal to or higher than the input shaft speed. Due to the fact that the driven shaft may be driven faster than the input shaft substantial speed reduction is required between the driven shaft with the second variable drive pulley and the axle shafts.
The speed reduction systems used in the past have required substantial space which is not available in many vehicle applications. The single stage speed reduction also reduces the ability to change the fixed ratios.